1. Field of the Invention
The present invention relates to an optical head apparatus comprising first and second laser diodes to emit laser lights adapted to different first and second recording media, respectively, wherein a laser driver for driving the first and second laser diodes is placed in an optical housing in which the first and second laser diodes are incorporated.
2. Description of the Related Art
An optical head apparatus which applies laser light to a recording medium such as a disk to optically read and/or write signals includes an apparatus that comprises a plurality of kinds of different laser diodes to emit laser lights having wavelengths suitable for recording densities of recording media so as to accommodate the recording media having different recording densities, for example, both a DVD and a CD.
Such an optical head apparatus comprising the plurality of laser diodes may be separately provided with laser driving semiconductor integrated circuits (laser drivers) which configure the laser drivers for driving laser diodes, or may be provided with a single laser driver having laser driver functions to drive the respective laser diodes. At present, the latter mode is common (refer to Japanese Patent Publication Laid-open No. 2003-99969).
In the meantime, the optical head apparatus is supported movably in a direction traversing a signal track of the recording medium. A flexible circuit board is used to connect the optical head apparatus to a circuit board installed in an equipment main body in which the optical head apparatus is mounted. This flexible circuit board is used to communicate electric signals across various kinds of electrical components mounted on the optical head apparatus and the above-mentioned circuit board.
In the flexible circuit board, various electrical components are mounted along the optical head apparatus in an area attached to the optical head apparatus. More specifically, the laser diodes incorporated into the optical head apparatus, a photo-detector which receives laser light reflected from the recording medium, a front monitor diode to monitor the amount of emission from the laser diodes, and the like are connected.
Furthermore, as the laser driver needs to be disposed in proximity to the laser diodes to reduce deterioration of drive pulse signals and effects of undesirable radiation, it is also, in many cases, disposed in and connected to the area of the flexible circuit board attached to the optical head apparatus.
The positions of the various electrical components mounted on the optical head apparatus are set considering the outer shape of the optical head apparatus, an optical layout and a connection relation among the various electrical components or considering that the flexible circuit board will be bent. Moreover, the size is limited depending on the outer shape of the optical head apparatus, so that the flexible circuit board will have a complicated shape in which connection portions to be connected to the respective electrical components branch in all directions.
Incidentally, the optical head apparatus adapted to record and reproduce signals of DVDs and CDs is generally provided with laser diodes exclusive to DVDs and CDs, respectively. The DVD laser diode and CD laser diode are often arranged away from each other on the optical head apparatus in relation to the optical layout.
As there is a dual wavelength semiconductor laser which emits laser lights at different wavelengths, it is contemplated that this dual wavelength semiconductor laser could be used to conform to DVDs and CDs. On the other hand, a disk standard has recently emerged which uses a blue laser beam to record and reproduce high-density signals. If an optical head apparatus conforming to this high-density disk standard is provided, compatibility is required with DVDs and CDs which are not high density. Therefore, a plurality of semiconductors are required after all, and a plurality of laser diodes are disposed at separate positions of the optical head apparatus.
When the single laser driver drives a plurality of laser diodes, it is difficult to dispose the laser driver in proximity to all the laser diodes. This leads to problems including waveform deformation of the drive pulse signals caused by the laser diodes being disposed away from the laser driver and undesirable radiation attributable to the drive pulse signals.
On the other hand, when the laser drivers adapted to a plurality of laser diodes are used to independently drive the respective laser diodes, it is difficult to secure areas to place the plurality of laser drivers on the flexible circuit board.
Japanese Patent Publication Laid-open No. 2003-99969 mentioned above shows an optical head apparatus wherein a laser driver is provided which has, at final stages, a plurality of amplifier circuits to amplify a current for each laser diode and wherein the final stages are selectively operated to drive a desired laser diode. This can prevent the waveform deformation of the drive pulse signals by disposing each of the final stages in the proximity of the corresponding laser diode.
However, the optical head apparatus disclosed in Japanese Patent Publication Laid-open No. 2003-99969 mentioned above only shows that the laser driver is placed in the optical head apparatus, and does not have any concept to place the laser driver on the flexible circuit board. In addition, a switching circuit which selectively operates the final stage corresponding to each of the laser diodes is not disposed in the proximity of each of the laser diodes. Thus, since the level of currents running from the final stages via the switching circuit will be the current level of the drive pulse signals which drive the laser diodes, the problem of the undesirable radiation attributed to the drive pulse signals is not solved.
Furthermore, the laser diodes for ultra-red laser and a red laser used for CDs and DVDs have different on-voltages depending on the kind. For this reason, when a common laser driver is used to drive the respective laser diodes, the power supply voltage of the laser driver needs to be set in accordance with the one with a higher on-voltage. In this case, due to the power wastefully consumed in the driving of the CD laser diode conforming to the laser diode with a lower on-voltage, the power consumption of the laser driver is increased.
The increase in the power consumption at the laser driver directly leads to a problem in heat generation, which requires some measures to be taken. In particular, the on-voltage of the blue laser diode conforming to the high-density disk standard described above is further higher than that of a laser diode for red laser light. Therefore, if the laser driver to drive the laser diodes for the ultra-red laser and red laser is used in common to drive the blue laser diode, the power supply voltage of the laser driver needs to be further increased. If the laser diodes for the ultra-red laser and red laser are driven in that state, the power wastefully consumed in the laser driver is further increased, and heat generation will be a more serious problem.